The muscles of the back can be divided into three groups – superficial, intermediate and intrinsic. The superficial muscles are associated with movements of the shoulder, the intermediate muscles with movements of the thoracic cage, and the deep muscles with movements of the vertebral column. The deep muscles develop embryologically in the back and are thus considered intrinsic. The superficial and intermediate muscles do not develop in the back, and are classified as extrinsic.
The deep muscles of the back are well-developed and extend from the sacrum to the base of the skull. These muscles are associated with the movement of the vertebral column and the control of posture. They are also covered by deep fascia, which plays an important role in their organisation.
Anatomically, the deep back muscles can be divided into three layers; superficial, intermediate and deep. We shall now look at each layer in more detail.
The superficial muscles are also known as the spinotransversales and there are two muscles in this group – splenius capitis and splenius cervicis. Both muscles are associated with the movement of the head and neck and are located on the posterolateral aspect of the neck, covering the deeper neck muscles.
Note – The two splenius muscles can also act together to extend the head and neck.
The intermediate muscles are also known as the erector spinae, and there are three muscles in this group – the iliocostalis, longissimus and spinalis. The erector spinae is situated posterolaterally to the spinal column, between the vertebral spinous processes and the costal angle of the ribs. All three muscles can be sub-divided by their superior attachments (into lumborum, thoracic, cervicis and capitis). They also have a common tendinous origin, which arises from the lower thoracic and lumbar vertebrae, the sacrum, the posterior aspect of the iliac crest and the sacroiliac and supraspinous ligaments.
The spinalis muscle is located medially within the erector spinae, and is the smallest of the three muscle columns. It can be divided into the thoracic, cervicis and capitis (although the cervicis part is absent in some individuals).
The deep muscles of the back are an intricate and integral part of the body's musculoskeletal system, and are essential for normal body movement, posture and support. A detailed understanding of their anatomy is essential for correct diagnosis and treatment of any pathology involving these muscles.
This article focuses on the anatomy of the deep (intrinsic) back muscles - their attachments, innervations and functions. These deep muscles of the back are well-developed, extending from the sacrum to the base of the skull, and are associated with the movements of the vertebral column and the control of posture.
Anatomically, the deep back muscles can be divided into three layers; superficial, intermediate and deep. The superficial layer is also known as the spinotransversales and consists of two muscles - splenius capitis and splenius cervicis. These are situated on the posterolateral aspect of the neck and cover the deeper neck muscles. Splenius capitis originates from the lower aspect of the ligamentum nuchae, and the spinous processes of C7 - T3/4 vertebrae, attaching to the mastoid process and the occipital bone of the skull. It is innervated by the posterior rami of spinal nerves C3 and C4, and its action is to rotate the head to the same side.
The intermediate back muscles are located posterolaterally to the spinal column and are referred to as the erector spinae. These are composed of three muscles - the iliocostalis, longissimus and spinalis. The iliocostalis muscle originates from the costal angle of the ribs and the cervical transverse processes, acting unilaterally to laterally flex the vertebral column and bilaterally to extend the vertebral column and head. The longissimus muscle originates from the lower ribs, the transverse processes of C2 - T12, and the mastoid process of the skull, and also acts unilaterally to laterally flex the vertebral column and bilaterally to extend the vertebral column and head. The spinalis muscle is located medially within the erector spinae, attaching to the spinous processes of C2, T1-T8 and the occipital bone of the skull, performing the same functions as the iliocostalis and longissimus muscles.
The deep (intrinsic) back muscles are located underneath the erector spinae and are referred to as the transversospinales. These consist of three major muscles - the semispinalis, multifidus and rotatores. The semispinalis is the most superficial of the deep intrinsic muscles, originating from the transverse processes of C4-T10, ascending 4-6 vertebral segments and attaching to the spinous processes of C2-T4 and to the occipital bone of the skull. It is designed to extend and contralaterally rotate the head and vertebral column. The multifidus is located underneath the semispinalis muscle and has a broad origin - arising from the sacrum, posterior iliac spine, common tendinous origin of the erector spinae, mamillary processes of lumbar vertebrae, transverse processes of T1-T3 and articular processes of C4-C7, and its fibres ascend 2-4 vertebral segments, attaching to the vertebral spinous processes. Its role is to stabilise the vertebral column. The rotatores are the deepest muscles of the transversospinales group, most prominent in the thoracic region, and they originate from the vertebral transverse processes.
In conclusion, the muscles of the back can be divided into three groups - superficial, intermediate and deep (intrinsic). The superficial back muscles consist of the spinotransversales and the intermediate back muscles are known as the erector spinae. The deep intrinsic back muscles are divided into two groups - the erector spinae and the transversospinales. The erector spinae muscle group consists of the iliocostalis, longissimus and spinalis muscles, while the transversospinales muscle group consists of the interspinalis, intertransversarii, multifidus and semispinalis muscles.
The deep intrinsic back muscles play a vital role in maintaining posture, stability, and joint coordination. The two main groups of muscles are the multifidus and semispinalis muscles, which originate from the transverse processes of the vertebrae and attach to the spinous processes of the vertebrae above. Another group of muscles is the levatores costarum, which originate from the transverse processes of C7-T11 and attach to the rib immediately below, acting to elevate the ribs.
The functions of the deep intrinsic back muscles include:
The deep intrinsic back muscles are innervated by the posterior rami of the spinal nerves. This means they are able to receive sensory signals from the central nervous system, enabling the muscles to quickly respond to changes in position and coordinate movements accordingly.
Due to their intimate connection with the spine, the deep intrinsic muscles serve a number of important functions such as:
The deep intrinsic back muscles are also involved in controlling the balance of the body. As a result, when the deep intrinsic muscles are weakened, the body is more likely to lose its natural stability and become vulnerable to injury. Without the support of these muscles, the spine does not respond optimally to movements, leading to increased strain and discomfort in the muscles, joints, and ligaments.
The deep intrinsic back muscles are essential for maintaining functional movement and avoiding injury. As such, they must be effectively trained in order to achieve optimal performance. Strength training is the key to developing strong intrinsic back muscles and should be done in combination with stretching and flexibility exercises. Resistance training is important as it allows the muscles to build up strength subtly over time, allowing them to become more responsive and resilient, aiding in injury prevention.
By properly training and strengthening the deep intrinsic back muscles, athletes can improve their performance and reduce the risk of injuries. Overall, these muscles are extremely important for providing stability and support to the spine, and should be trained and maintained in order to ensure optimal wellbeing.
